Download EMI in the Workplace Environment

EMI in the Workplace Environment
Medical devices have become very sophisticated since the introduction of the first
implantable pacemaker in the late 1950’s. Similarly, technology of items found in the
home and workplace environments have become very sophisticated to the point where
interaction between some products and implanted devices can occur. Mechanical and
electrical shielding designed into pacemakers and implantable cardioverter-defibrillators
(ICDs), has, in most cases, enabled these medical devices to be immune to external
electromagnetic interference (EMI). Most of the common home and workplace items
that can generate EMI typically do not interfere with normal operation of implantable
medical devices.
There are instances where equipment in a home, workplace or other environment may
produce levels of electromagnetic interference capable of interfering with an implantable
pacemaker or ICD. When interference is encountered, there are various device
responses (some of which are listed below) that can occur and are usually temporary
until the source of the EMI is removed or the patient moves outside the EMI field. If
interference is encountered, once the patient is no longer exposed to the EMI field,
normal device function usually returns. In the event that an EMI source strong enough
to affect an implanted device is encountered, one or more of the potential responses
listed in Table 1 below may occur.
Table 1 – Potential device responses.
Response
A description of each is outlined in the bullets below.
Asynchronous pacing/ Magnet mode operation
Inhibition
Tracking up to programmed Maximum Rate
Inappropriate shocks/ATP
Inhibition of High Voltage/ATP therapy
Device Damage
•
•
•
•
•
•
Pacemakers
ICDs
Possible
Possible
Possible
N/A
N/A
Unlikely
Possible
Possible
Possible
Possible
Possible
Unlikely
Asynchronous pacing due to electrical noise is a safety feature that forces pacing regardless of the patient’s
own rhythm. Magnet mode will also cause asynchronous pacing in response to a magnetic field in
pacemakers.
Inhibition of pacing (pauses in pacing) may occur at the onset of noise or with continued noise.
In dual chamber devices noise detected on the atrial channel may result in temporary increased ventricular
paced rates within the programmed limits.
Noise could inhibit or trigger high voltage/Anti-Tachycardia Pacing (ATP) therapy.
The presence of a static magnetic field may inhibit shock therapy.
An external high voltage shock may result in device damage. This type of interference is not specified in the
Field Strength Test Limits table below.
The susceptibility of an implanted device being affected by the environment or an
external source of EMI is influenced by many factors including the patient body mass,
the implanted device configuration and programmed settings, the proximity and
orientation to the EMI field as well as the EMI field strength.
October 2011
Technical Services
15900 Valley View Court
Sylmar, CA 91342 USA
800-722-3774
Page 2 of 4
For patients who work in, or frequent locations that may expose them to high levels of
electromagnetic interference, specific testing of an environment should be undertaken if
a medical professional deems there is sufficient risk to the patient based on the patient’s
medical history.
St. Jude Medical does not provide field testing of potential sources of interference.
Patients who work at facilities where EMI sources may be present should consider
advising their employer that they have an implanted medical device and that
environmental testing may be in order. This type of assessment can be performed by a
trained EMI testing consultant at the employer’s request. Testing typically includes the
work areas the employee would encounter, but may include the entire facility as the
employer and tester deem necessary. A list of some potential EMI test consultants is
provided to help facilitate this testing. St. Jude Medical does not recommend any
particular consultant nor do we ensure the quality of the EMI testing performed. EMI
field strengths encountered above those listed in Table 2 may cause device interference
with an undesired device response.
Table 2 - Field Strength Test Limits
EMI Source
High Voltage Power Lines (50/60 Hz)
Continuous Wave and/or Modulated
Magnetic Fields (50/60 Hz)
Static Magnetic Field
Field type Field strength limit
E-field
6000 V/m peak
H-field
80 A/m peak
B-field
5 Gauss (0.5 mT) peak
The above mentioned H-field limit will vary depending on the frequency of the EMI. Further standards
may be reviewed for other frequencies in the International Non-Ionizing Radiation Protection (ICNIRP)
recommendations for reference levels for general public exposure to time-varying electric and magnetic
fields.
•
•
•
The H-field limit is useful in ensuring that a time varying magnetic field will not
induce electrical voltages or currents in the lead-device-tissue loop area. Any
induced electrical signals should be below the device sensing threshold, and well
below the capture threshold just as for an E-field.
The B-field limit is useful in ensuring that the device magnet mode (using the
GMR – Giant MagnetoResistive sensor) will not activate. The formal standard is
that a device shall not detect environmental fields less than or equal to 10Gauss
(1 milliTesla). The clinical field magnets are much stronger, about 125Gauss at
one inch distance to ensure properly activating the sensor when desired.
Some commercially available measuring instruments may switch between H
units (Amperes/meter or Oersteds) and B units (Gauss or Tesla). Different
equipment is needed to measure H- or B-fields. H-fields require frequency and
area to be accounted for. Therefore different probes (antenna) will be required to
make the measurements.
St. Jude Medical pacemakers and ICDs are designed to meet the electromagnetic
compatibility requirements described in the following standards:
October 2011
Technical Services
15900 Valley View Court
Sylmar, CA 91342 USA
800-722-3774
Page 3 of 4
European Standard EN 45502-2-1
Active Implantable Medical Devices Part 2-1: Particular requirements for active implantable medical
devices intended to treat bradyarrhythmia (Cardiac pacemakers).
European Standard prEN 45502-2-2
Active Implantable Medical Devices, Part 2-2: Particular requirements for active implantable medical
devices intended to treat tachyarrhythmia (includes implantable defibrillators).
nd
2007 American National Standard ANSI/AAMI PC69, 2 edition
Implantable Medical Devices – Electromagnetic compatibility.
St. Jude Medical does not provide recommendations regarding a patient’s ability to
return to work because we can not account for every variable or unique condition in the
workplace environment. Technical Services can provide technical assistance to the
employer or testing consultant in interpreting test results related to various EMI sources
and potential responses.
If you need additional information or would like to discuss this subject further, please call
Technical Services at 1-800-722-3774, or for Europe at +46-8474-4147.
October 2011
Technical Services
15900 Valley View Court
Sylmar, CA 91342 USA
800-722-3774
Page 4 of 4
Environmental EMI testing Consultants
DNB Engineering
Fullerton, CA
(800) 282-1462
Doug Broaddus
WEB: www.dnbenginc.com
Wyle Laboratories
Huntsville, AL
256-837-4411
Bobby Hardy
WEB: www.wylelabs.com
EF Electronics
Aurora, IL
630-897-1950
Ed French
EMAIL: [email protected]
American Industrial Hygiene Association
Fairfax, VA
703-849-8888
WEB: www.aiha.org
Radiometrics Midwest Corporation
Romeoville, IL
815-293-0772
WEB: www.radiomet.com
Dave Baron, PE
Consulting Engineer
Electromagnetic Field Safety
Austin, TX 512-917-8346
Minneapolis MN 612-722-4027
EMAIL: [email protected]
EMF Testing Services
Indianapolis, IN
800-862-9655
Stuart Bagley
WEB: www.emftesting.net
EMAIL: [email protected]
October 2011
Technical Services
15900 Valley View Court
Sylmar, CA 91342 USA
800-722-3774